1. Field of the Invention
This invention relates to the production of polyalkylene polyamines, and more particularly to a process for enhancing the production of predominantly linearly extended polyalkylene polyamines while substantially avoiding the production of heterocyclic by-products.
2. Description of the Prior Art
Several patents, including, for example U.S. Pat. Nos. 4,036,881 (Brennan I) and 3,044,053 (Brennan II), disclose the preparation of predominantly non-cyclic polyalkylene polyamines from the condensation of an alkanolamine or alkylene glycol compound with an alkylenediamine compound. These patents, however, disclose that it is not critical to control the amount of water present during the heating of reactants and catalyst. For example, Brennan I discloses from column 5, line 65 to column 6, line 3 that "it is not critical to control the amount of water of reaction present during the heating of reactants and catalyst, such as by removal thereof as it is formed. Usually, we prefer to retain water in the reaction zone and remove it from the reaction mass during recovery of the predominantly non-cyclic polyalkylene polyamines." It is therefore disclosed that a preferred embodiment of the Brennan process is to retain water in the reaction zone and remove it from the reaction mass during recovery of the product. In addition, the disclosed process even provides for the addition of water to the reaction mass to generate an aqueous solution for conducting the process, such as described in Example II in Brennan I.
It has been discovered, in direct contradiction to these disclosures, that not only is water removal desirable during the production of predominantly non-cyclic polyalkylene polyamines using a phosphorus catalyst, but that water removal provides for enhanced conversion rates of the reactants.
Although not wishing to be bound to any particular theory, a basis for this discovery of increased conversion rates when water is removed from the reaction zone may be as follows. A schematic representation for the process of the present invention, as well as the process in the Brennan patents, is presented in Formula I below: ##STR1## This overall equation is irreversible in that the alkylated amine product does not readily react with water to generate an amine and a hydroxy compound. For this reason, it cannot be predicted from this overall equation that the presence of water would be a contributing factor in reaction efficiency. Instead, it was well established in the prior art, through the Brennan patents, that water was not a critical component in the overall process.
It is believed, however, that an intermediate step not appreciated by the prior art, identified by Formula III below, is responsible for establishing the criticality of the presence of water during the reaction. According to the theory a reversible reaction exists, as an intermediate step to the formulation of polyalkylene polyamines, in which the phosphorus catalyst or acid intermediate condenses with the hydroxy reactant to form a phosphorus ester as shown in Formula II: ##STR2## in which X is a radical as hereinafter defined including hydroxyl, amide, or halo groups. The phosphorus ester may subsequently enter into a similar equilibrium with water according to Formula III: ##STR3## Obviously when X is a hydroxyl group, Formula II merges with Formula III for phosphorus acid catalysts. Since this reaction is reversible, removal of water, added previously or formed during the reaction, shifts the equilibrium towards the formation of the phosphorus ester. The increased concentration of this ester is believed to be responsible for providing increased conversion rates to linearly extended polyalkylene polyamines.
Water removal has been disclosed in various amine production processes. For example, U.S. Pat. No. 3,121,115 (Meuly) contains a disclosure for the production of aminoalkylated compounds containing tertiary amino groups. The disclosed process involves reacting alkylatable amines or phenols with N-tertiary aminoalkanols in the presence of a phosphoric acid catalyst. There is no disclosure of an alkylenediamine reactant, since the patent is limited to specifically describing monoamines or aromatic diamines. There is also no disclosure of a difunctional alkylene glycol or alkanolamine reactant, since the patent is specifically limited to monofunctional, tertiary aminoalkanol reactants. As a consequence, there is no production of predominantly linearly extended polyalkylene polyamines, nor is there any appreciation for the formation of cyclic compounds, since the patent does not relate to polycondensation reactions upon which the formation of cyclic compounds is based. Similarly, U.S. Pat. No. 4,103,087 (Brennan III) presents an improved process for reacting tertiary aminoalkanols with monofunctional secondary amines to produce a di-(N,N-disubstituted amino)alkane product. Both patents are distinguishable from the process of the present invention since their disclosures of water removal for amine condensation reactions in general does not present evidence to contradict the specific teaching in the Brennan patents that polyalkylene polyamine condensation reactions are not dependent upon water concentration. There is no indication or suggestion in the Brennan III or Meuly patents that intermediate reactions in the production of polyalkylene polyamines involving difunctional alkylene glycol or alkanolamine compounds would be reversible, thereby establishing a dependency upon water concentration.
Water removal has also been disclosed in other amine production processes, such as in U.S. Pat. Nos. 4,210,605 (Hoshino et al) and 4,254,060 (Kimura et al) in order to avoid the deactivation of particular homogeneous, metal containing, colloidal catalysts. These patents do not relate to condensation reactions involved in the production of polyalkylene polyamines, such that there is no appreciation that specific intermediate steps may be dependent upon water condensation.
U.S. Pat. No. 3,714,259 (Lichtenwalter et al) discloses an alternative process for the production of linear polyalkylene polyamines using a hydrogenation catalyst. There is no disclosure of water removal, or that the use of a phosphorus-containing catalyst would create a dependency on water concentration.